Field of the Invention
A structural support beam for use in buildings, bridges, automotive frames and the like.
Description of the Prior Art
A beam is a structural element that is capable of withstanding load primarily by resisting bending. The bending force induced into the material of the beam as a result of the external loads, own weight, span and external reactions to these loads is called a bending moment.
Beams are traditionally descriptions of building or civil engineering structural elements, but smaller structures such as truck or automobile frames, machine frames, and other mechanical or structural systems contain beam structures that are designed and analyzed in a similar fashion.
In engineering, beams are of several types:                Simply supported—a beam supported on the ends which are free to rotate and have no moment resistance.        Fixed—a beam supported on both ends and restrained from rotation.        Over hanging—a simple beam extending beyond its support on one end.        Double overhanging—a simple beam extending beyond its supports ends.        Continuous—a beam extending over more than two supports.        Cantilever—a projecting beam fixed only at one end.        Trussed—a beam strengthened by adding a cable or rod to form a truss.        
Most beams in reinforced concrete buildings have rectangular cross sections, but a more efficient cross section for a beam is an I or H section which is typically seen in steel construction. Because of the parallel axis theorem and the fact that most of the material is away from the neutral axis, the second moment of area of the beam increases, which in turn increases the stiffness.
An I-beam is only the most efficient shape in one direction of bending: up and down looking at the profile as an I. If the beam is bent side to side, it functions as an H where it is less efficient. The most efficient shape for both directions is a box (a square shell) or tube. But, however the most efficient shape for bending in any direction is a cylindrical shell or tube. But, for unidirectional bending, the I or wide flange beam is superior.
Cross-sectional views of more typical configurations or shapes are depicted in FIG. 1A through FIG. 1F.
Internally, beams experience compressive, tensile and shear stresses as a result of the loads applied to them. Typically, under gravity loads, the original length of the beam is slightly reduced to enclose a smaller radius arc at the top of the beam, resulting in compression, while the same original beam length at the bottom of the beam is slightly stretched to enclose a larger radius arc, and so is under tension. The same original length of the middle of the beam, generally halfway between the top and bottom, is the same as the radial arc of bending, and so it is under neither compression nor tension, and defines the neutral axis dotted line in the beam figure. Above the supports, the beam is exposed to shear stress. There are some reinforced concrete beams in which the concrete is entirely in compression with tensile forces taken by steel tendons. These beams are known as prestressed concrete beams, and are fabricated to produce a compression more than the expected tension under loading conditions. High strength steel tendons are stretched while the beam is cast over them. Then, when the concrete has cured, the tendons are slowly released and the beam is immediately under eccentric axial loads. This eccentric loading creates an internal moment, and, in turn, increases the moment carrying capacity of the beam. They are commonly used on highway bridges.
The following references illustrate the prior art.
U.S. Pat. No. 1,843,318 discloses an arch comprising a curved lower chord having reinforcing bars 24 and 24′ secured at each side of the lower curved edge of the arch to absorb the thrust (see FIG. 16).
U.S. Pat. No. 4,831,800 relates to a beam and reinforcing member comprising a longitudinally extending beam having a concrete upper flange, a web having greater tensile strength than concrete and rigidly connected to the upper flange with shear connectors. The web extends transversely downward from the upper flange longitudinally spaced apart leg portions with an intermediate arched portion extending between the leg portions.
U.S. Pat. No. 4,704,830 shows a flexible tension load bearing member such as a chain strung alongside an I-beam web portion end to end and hooked over the top flange. The mid-section of the chain is then attached in a load bearing capacity to the lower flange, preferably by a post tension controlling adjustable link controlling the chain tension.
Additional examples are found in U.S. Pat. No. 3,010,257; U.S. Pat. No. 3,101,272; U.S. Pat. No. 3,283,464; U.S. Pat. No. 3,300,839; U.S. Pat. No. 3,535,768; U.S. Pat. No. 4,424,652; U.S. Pat. No. 4,576,849 and U.S. Pat. No. 5,125,207.